Techniques for improving control channel acquisition in a wireless communication system

ABSTRACT

A technique of operating a wireless communication system includes determining respective geometries of multiple subscriber stations, which include a first subscriber station and a second subscriber station, with respect to a serving base station. Respective control channels, which include a first control channel associated with the first subscriber station and a second control channel associated with the second subscriber station, for the multiple subscriber stations are then scheduled based on the respective geometries. The first control channel is scheduled to be encountered earlier in a control channel search procedure, of the one or more control channel symbols, than the second control channel. The first subscriber station has a lower geometry than the second subscriber station.

BACKGROUND

1. Field

This disclosure relates generally to control channels and, morespecifically, to techniques for improving control channel acquisition ina wireless communication system.

2. Related Art

In general, orthogonal frequency division multiplexing (OFDM) systemssupport high data rate wireless transmission using orthogonal channels,which offer immunity against fading and inter-symbol interference (ISI)without requiring implementation of elaborate equalization techniques.Typically, OFDM systems split data into N streams, which areindependently modulated on parallel spaced subcarrier frequencies ortones. The frequency separation between subcarriers is 1/T, where T isthe OFDM symbol time duration. Each symbol may include a guard interval(or cyclic prefix) to maintain the orthogonality of the symbols. Ingeneral, OFDM systems have utilized an inverse discrete Fouriertransform (IDFT) to generate a sampled (or discrete) compositetime-domain signal.

Wireless networks have generally used an estimated received signalstrength and an estimated carrier to interference and noise ratio (CINR)of a received signal to determine operational characteristics of thenetworks. As one example, IEEE 802.16e compliant mobile stations (MSs)are required to estimate a received signal strength indicator (RSSI) anda CINR of a received signal. The RSSI associated with a serving BS maybe used by an MS for cell re-selection and the CINR, which is reportedto the serving BS, may be used by the serving BS to adapt a downlinktransmission rate to link conditions.

Accurate reported CINRs are desirable, as inaccurate reported CINRs mayimpact performance of a wireless network. For example, reporting a CINRthat is above an actual CINR may decrease network throughput due toframe re-transmission, while reporting a CINR that is below the actualCINR may cause the serving BS to schedule data rates below a supportabledata rate. According to IEEE 802.16e, RSSI and CINR estimates at an MSare derived based on a preamble signal, which is an orthogonal frequencydivision multiple access (OFDMA) symbol that is transmitted at thebeginning of each OFDMA frame.

Similarly, wireless networks that employ third-generation partnershipproject-long term evolution (3GPP-LTE) compliant architectures arerequired to employ uplink reference signals (RSs) for uplink CINRestimation, which is used by the network to schedule uplink transmissionfor user equipment (subscriber stations (SSs)). Respective sequences ofthe RSs are used to uniquely identify an SS and, when transmitted fromthe SS to a serving base station (BS), may be used by the serving BS inchannel characterization. In general, a scheduler associated with one ormore serving BSs utilizes information derived from channelcharacterization to determine channel allocation for the SSs. Thechannel allocation, e.g., uplink and downlink assignments, have thenbeen provided to the SSs over a downlink shared control channel, whichtypically includes one or more control channel symbols. The one or morecontrol channel symbols may be transmitted by the serving BS at abeginning of a downlink frame (or subframe). Typically, upon receivingthe one or more control channels symbols, each of the SSs searches theone or more control channel symbols to determine an associated uplinkand downlink assignment. Known control channel scheduling approacheshave proposed scheduling control channels irrespective of an SSsgeometry with respect to a serving BS. Unfortunately, low-geometry SSs(e.g., cell-edge SSs operating at or near an edge of a cell) may receivea relatively weak signal from the serving BS and, thus, may experience arelatively high error rate in detecting associated control channels.Moreover, low-geometry SSs may also experience a relatively high latencyin detecting associated control channels.

What is needed are techniques for improving control channel acquisitionin a wireless communication system.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and is notlimited by the accompanying figures, in which like references indicatesimilar elements. Elements in the figures are illustrated for simplicityand clarity and have not necessarily been drawn to scale.

FIG. 1 is an example diagram of a downlik (DL) subframe, including twocontrol channel symbols, that may be transmitted from a serving basestation (BS) to multiple subscriber stations.

FIG. 2 is a flowchart of a control channel scheduling process that maybe, at least partially, employed in a scheduler in a wirelesscommunication system, according to the present disclosure.

FIG. 3 is a flowchart of a process for receiving one or more controlchannel symbols and searching the one or more control channel symbolsfor an associated control channel at a given subscriber station (SS) ina wireless communication system, according to the present disclosure.

FIG. 4 is an example diagram of a control channel search procedure fordetecting a control channel associated with an SS in a wirelesscommunication system.

FIG. 5 is a block diagram of an example wireless communication systemthat may schedule control channels for SSs according to variousembodiments of the present disclosure.

DETAILED DESCRIPTION

In the following detailed description of exemplary embodiments of theinvention, specific exemplary embodiments in which the invention may bepracticed are described in sufficient detail to enable those skilled inthe art to practice the invention, and it is to be understood that otherembodiments may be utilized and that logical, architectural,programmatic, mechanical, electrical and other changes may be madewithout departing from the spirit or scope of the present invention. Thefollowing detailed description is, therefore, not to be taken in alimiting sense, and the scope of the present invention is defined onlyby the appended claims and their equivalents. In particular, althoughthe preferred embodiment is described below in conjunction with asubscriber station, such as a cellular handset, it will be appreciatedthat the present invention is not so limited and may be embodied invarious wireless devices, e.g., personal digital assistants (PDAs),digital cameras, portable storage devices, audio players, computersystems, and portable gaming devices, for example.

As is used herein, the term “user equipment” is synonymous with the term“subscriber station,” which is used to broadly denote a wireless deviceassociated with a wireless communication system. As is also used herein,the term “control channel symbol” includes a symbol that occupies achannel, which may occupy an entire system bandwidth or a portion of theentire system bandwidth. The term “channel,” as used herein, includesone or more subcarriers, which may or may not be adjacent. As usedherein, the term “slot” refers to a symbol location in a multiple accesssignal. The term “blind search procedure” is used herein to refer to asearch procedure in which the searcher, e.g., an SS, has no priorknowledge of a location of an item searched for in a sequence of items.For example, when an SS is searching one or more control channel symbolsfor an associated control channel, the SS does not have prior know ofthe location of the associated control channel in the one or morecontrol channel symbols when a blind search procedure is employed.

According to various aspects of the present disclosure, a controlchannel scheduling technique is employed that generally reduces latencyand error rate associated with the detection of a control channel by alow-geometry subscriber station (SS). A geometry of an SS with respectto a serving base station (BS) may be indicated by, for example, acarrier-to-interference and noise ratio (CINR) associated with the SS.For example, a cell-edge SS may have a relatively low associated CINR ata serving BS and, thus, be classified as a low-geometry SS. In general,a low-geometry SS control channel is scheduled in one or more controlchannel symbols (transmitted from a serving BS on a common controlchannel) such that the low-geometry SS control channel may be detectedearlier in a control channel search procedure employed by thelow-geometry SS. For example, when a low-geometry SS employs a blindsearch procedure that starts at a beginning of the one or more controlchannel symbols and sequentially searches through the control channelsymbols until the low-geometry SS finds an associated control channel,the low-geometry SS control channel should be scheduled toward thebeginning of the one or more control channel symbols. It should,however, be appreciated that the techniques disclosed herein are equallyapplicable to search routines that do not sequentially search one ormore control channel symbols from beginning to end.

According to one embodiment of the present disclosure, a method ofoperating a wireless communication system includes determiningrespective geometries of multiple subscriber stations (SSs), whichinclude a first SS and a second SS, with respect to a serving basestation (BS). Respective control channels for the multiple SSs are thenscheduled based on the respective geometries. The respective controlchannels include a first control channel (associated with the first SS)and a second control channel (associated with the second SS). The firstcontrol channel is scheduled to be encountered earlier in a controlchannel search procedure (of one or more control channel symbols) thanthe second control channel. In this embodiment, the first SS has a lowergeometry than the second SS. Thus, in a typical case, a low-geometry SSshould detect an associated control channel relatively early in acontrol channel search procedure. This generally reduces the latencyassociated with a low-geometry SS detecting an assigned control channeland reduces the probability of the low-geometry SS detecting a wrongcontrol channel as an assigned control channel (which is commonlyreferred to as false positive probability). In at least one embodiment,the first control channel is scheduled in a first control channel symbol(included within the one or more control channel symbols) of a downlinkframe or subframe.

According to another embodiment of the present disclosure, a method ofoperating a wireless communication system includes receiving, at a firstsubscriber station (SS) a first control channel associated with thefirst SS and a second control channel associated with a second SS. Oneor more control channel symbols are searched by the first SS for thefirst control channel, which is scheduled such that the first controlchannel is encountered earlier in a control channel search procedure ofone or more control channel symbols than the second control channel. Inthis embodiment, the first SS has a lower geometry than the second SS.

According to another aspect of the present disclosure, a wirelesscommunication system includes a base station (BS) and a scheduler. TheBS is configured to determine respective geometries of multiplesubscriber stations (SSs) with respect to the BS. The multiple SSsinclude a first SS and a second SS. The scheduler is configured toschedule respective control channels for the multiple SSs based on therespective geometries of the multiple SSs. The respective controlchannels include a first control channel associated with the first SSand a second control channel associated with the second SS. The firstcontrol channel is scheduled to be encountered earlier in a controlchannel search procedure of one or more control channel symbols than thesecond control channel. According to this aspect of the presentdisclosure, the first SS has a lower geometry than the second SS.

With reference to FIG. 1, an example downlink (DL) subframe 100 isillustrated that includes two control channels symbols 102 and multipledata symbols 104. The control channel symbols 102 include a number ofcontrol channel elements (CEs) each of which include a number ofsubcarriers, e.g., six subcarriers. Similarly the data symbols 104 eachinclude a number of resource blocks (RBs), e.g., twelve subcarriers. Itshould be appreciated that the CEs and the RBs may have the same size ora different size. It should also be appreciated that the techniquesdisclosed herein are broadly applicable to DL subframes of varying sizesand that a control channel symbol may assume an integer value (e.g., 1,2, 3, etc. symbols) or a fractional value (e.g., 1.5, 2.5, etc.symbols). Transmitters implemented within a wireless communicationsystem, configured according to various embodiments of the presentdisclosure, may transmit information using a phase shift keying (PSK), aquadrature amplitude modulation (QAM), or other data modulation scheme,depending upon which modulation scheme is scheduled. For example, any ofthe various PSK (such as pi/2 BPSK, QPSK, and 8-PSK), or QAM (such as16-QAM and 64-QAM) modulation techniques may be implemented.

According to various aspects of the present disclosure, respectivecontrol channels for subscriber stations (SSs) are scheduled in one ormore control channel symbols, based upon respective geometries of theSSs with respect to a serving base station (BS). For example, a controlchannel for a high-geometry SS (e.g., an SS with a CINR of about 15 dB)is scheduled to be encountered later in a control channel searchprocedure than a control channel for a low-geometry SS (e.g., an SS witha CINR of about 0 dB) that uses, for example, the same number of controlchannel elements (CEs). Moreover, a control channel for amedium-geometry SS (e.g., an SS with a CINR of about 7.5 dB) may bescheduled to be encountered earlier in a control channel searchprocedure than a control channel for a high-geometry SS that uses, forexample, the same number of control channel elements (CEs), and may bescheduled to be encountered later in a control channel search procedurethan a control channel for a low-geometry SS that uses, for example, thesame number of CEs. It should be appreciated that the CINRs, set forthabove, are example CINRs and that the detection may be based upon thenumber of CEs used in a control channel search procedure, or othercriteria. For example, control channels may be scheduled irrespective ofthe number of the number of CEs in a control channel.

In the disclosed approach, the serving BS initially calculates a CINR ofa training signal transmitted from a given SS, during a trainingsequence, and compares the calculated CINR to one or more thresholds todetermine a geometry of the given SS. The training signal may be, forexample, a random access preamble or a channel sounding burst. In theevent that a given SS is determined to be a low-geometry SS, a controlchannel for the given SS is assigned, by a scheduler, e.g., a networkscheduler, such that the given SS encounters the control channelscheduled for the given SS relatively early in a control channel searchprocedure of one or more control channel symbols. In the event that agiven SS is later detected to be at a higher geometry, the scheduler mayadjust the placement of later control channels for the given SS suchthat the given SS encounters the later control channels for the given SSlater in the control channel search procedure.

Turning to FIG. 2, a control channel scheduling process 200, that maybe, at least partially, employed in a scheduler (such as a network-basedscheduler) in a wireless communication system, is depicted. The process200 is initiated at block 202, at which point control transfers todecision block 204. In block 204, a serving base station (BS) determineswhether a training signal has been received from a subscriber station(SS). If a training signal is received in block 204, control transfersto block 206, where a CINR for the SS is determined based on thetraining signal. If a training signal is not received in block 204,control loops on block 204 until a training signal is received.Following block 206, control transfers to block 208, where the SS and anassociated CINR of the SS are added to an active SS table (e.g., amemory). In this manner, a geometry associated with a given SS may betaken into account when control channel symbols are being constructed.Next, in block 210, a scheduler utilizes the information included in thetable to schedule control channels for active SSs in one or more controlchannel symbols. It should be appreciated that information for activeSSs would typically be periodically updated and that information forinactive SSs would typically be periodically removed from the table.Following block 210, control transfers to block 212, where the servingBS transmits the control channel symbol(s) to the active SSs. Next,control transfers from block 212 to block 214, where control returns toa calling routine.

A CINR of a received signal may be estimated through a number ofapproaches. As a first example, U.S. Patent Application Publication No.2006/0133260 discloses a channel estimation based approach forestimating CINR that isolates noise and interference components usingpilot sequences and estimates a channel power by subtracting a combinednoise and interference power estimate from a received power estimate. Asa second example, U.S. Patent Application Publication No. 2006/0093074discloses a difference based approach for estimating CINR that assumesthat adjacent pilot locations have the same subchannel characteristics.In view of this assumption, noise and interference components areisolated by subtracting adjacent received signals.

Moving to FIG. 3, a process 300, for receiving one or more controlchannel symbols at a given SS and searching for an associated controlchannel for the given SS, is illustrated. In block 302, the process 300is initiated, at which point control transfers to block 304. In block304, one or more control channels symbols are received at an SS. Thecontrol channel symbols may be, for example, orthogonal frequencymultiplexing (OFDM) signals. Next, in block 306, the SS searches thecontrol channel symbols for an associated control channel, which mayinclude one or more control channel elements (CEs). The associatedcontrol channel may be a downlink control channel, an uplink controlchannel, or a combined control channel that includes both uplink anddownlink assignment information. Then, in block 308, information iseither transmitted by the SS in an assigned uplink or information isreceived by the SS in an assigned downlink. Typically, the assigneduplink (provided in an uplink control channel) includes an uplinksubcarrier assignment and an uplink slot assignment and the assigneddownlink (included in a downlink control channel) includes a downlinksubcarrier assignment and a downlink slot assignment. Following block308, control transfers to block 310, where control returns to a callingroutine. In general, scheduling low-geometry SSs to encounter anassociated control channel earlier in a control channel search proceduredecreases the probability of low-geometry SSs detecting a wrong controlchannel and decreases a time period required for the low-geometry SS tolocate an associated control channel. This is particularly advantageousfor cell-edge SSs which frequently receive weaker signals and experiencehigher interference (from, for example, non-serving BSs in neighboringcells).

Turning to FIG. 4, a chart of an example control channel searchprocedure, for detecting a control channel associated with an SS in awireless communication system, is depicted. In the illustrated controlchannel search procedure, an SS first searches single CEs (i.e., each ofCE1-CE6) for an associated control channel. Assuming that the SS doesnot find the associated control channel in a single CE, the SS searchestwo CEs (i.e., CE1/CE2, CE3/CE4, and CE5/CE6) for the associated controlchannel. Similarly, assuming that the SS does not find the associatedcontrol channel in two CEs, the SS searches three CEs (i.e., CE1/CE2/CE3and CE4/CE5/CE6) for the associated control channel. It should beappreciated that any number of different control channel searchprocedures may be employed by an SS. For example, a control channelsearch procedure may search for a control channel for a given SS byfirst searching a first CE of a control channel symbol for an associatedcontrol channel, then the first two CEs (i.e., the first CE and a secondCE) of the control channel symbol and then the first three CEs (i.e.,the first and second CEs and a third CE) of the control channel symbol.Assuming that the given SS does not find an associated control channel,the search procedure may search the second CE, then the second and thirdCEs and finally the second and third CEs and a fourth CE. In FIG. 4, acontrol channel (CCH) for a low-geometry SS that includes a single CE isscheduled to be located at CCH candidate 1. As is also illustrated,control channels for high-geometry SSs that include a single CE arescheduled at CCH candidate 2, CCH candidate 5, and CCH candidate 6,which are later than CCH candidate 1. A control channel for alow-geometry SS that includes two CEs is scheduled to be located at CCHcandidate 8, which, while being located after single CEs in controlchannel search procedure, is located prior to any higher geometry SSs(in this case zero) control channels that require two CEs in the controlchannel search procedure.

As noted above, scheduling low-geometry SSs to encounter an associatedcontrol channel earlier in a control channel search procedure usuallydecreases the probability of low-geometry SSs detecting a wrong controlchannel and usually decreases a search time period required for thelow-geometry SSs to find an associated control channel. As is also notedabove, this is particularly advantageous for cell-edge SSs whichfrequently receive weaker signals and frequently experience higherinterference from non-serving BSs in neighboring cells. It should beappreciated the control channel search procedure illustrated in FIG. 4may be applied to control channel symbols including more or less thansix CEs. Furthermore, it should be appreciated that the techniquesdisclosed herein are broadly applicable to other control channel searchprocedures.

With reference to FIG. 5, an example wireless communication system 500is depicted that includes a plurality of wireless devices (subscriberstations) 502, e.g., hand-held computers, personal digital assistants(PDAs), cellular telephones, etc., that may implement scheduling ofcontrol channels within a control channel symbol according to one ormore embodiments of the present disclosure. In general, the wirelessdevices 502 include a processor 508 (e.g., a digital signal processor(DSP)), a transceiver 506, and one or more input/output devices 504(e.g., a camera, a keypad, display, etc.), among other components notshown in FIG. 5. As is noted above, according to various embodiments ofthe present disclosure, techniques are disclosed that facilitateimproved control channel acquisition for a wireless communicationdevice, such as the wireless devices 502. The wireless devices 502communicate with a base station controller (BSC) 512 of a base stationsubsystem (BSS) 510, via one or more base transceiver stations (BTS)514, to receive or transmit voice, data, or both voice and data. The BSC512 may, for example, be configured to schedule communications for thewireless devices 502. Alternatively, the BTS 514 may schedulecommunications for the wireless devices 502 in which the BTS 514 is incommunication.

The BSC 512 is also in communication with a packet control unit (PCU)516, which is in communication with a serving general packet radioservice (GPRS) support node (SGSN) 522. The SGSN 522 is in communicationwith a gateway GPRS support node (GGSN) 524, both of which are includedwithin a GPRS core network 520. The GGSN 524 provides access tocomputer(s) 526 coupled to Internet/intranet 528. In this manner, thewireless devices 502 may receive data from and/or transmit data tocomputers coupled to the Internet/intranet 528. For example, when thedevices 502 include a camera, images may be transferred to a computer526 coupled to the Internet/intranet 528 or to another one of thedevices 502. The BSC 512 is also in communication with a mobileswitching center/visitor location register (MSC/VLR) 534, which is incommunication with a home location register (HLR), an authenticationcenter (AUC), and an equipment identity register (EIR) 532. In a typicalimplementation, the MSC/VLR 534 and the HLR, AUC, and EIR 532 arelocated within a network and switching subsystem (NSS) 530, which mayalso perform scheduling for the system 500. The SGSN 522 may communicatedirectly with the HLR, AUC and EIR 532. As is also shown, the MSC/VLR534 is in communication with a public switched telephone network (PSTN)542, which facilitates communication between wireless devices 502 andland telephones 540. It should be appreciated that other types ofwireless systems, having different configurations, may implement variousaspects of the control channel scheduling techniques disclosed herein.

Accordingly, a number of techniques have been disclosed herein thatgenerally improve control channel acquisition by subscriber stations ina wireless communication system.

As used herein, a software system can include one or more objects,agents, threads, subroutines, separate software applications, two ormore lines of code or other suitable software structures operating inone or more separate software applications, on one or more differentprocessors, or other suitable software architectures.

As will be appreciated, the processes in preferred embodiments of thepresent invention may be implemented using any combination of computerprogramming software, firmware or hardware. As a preparatory step topracticing the invention in software, the computer programming code(whether software or firmware) according to a preferred embodiment willtypically be stored in one or more machine readable storage mediums suchas fixed (hard) drives, diskettes, optical disks, magnetic tape,semiconductor memories such as read-only memories (ROMs), programmableROMs (PROMs), etc., thereby making an article of manufacture inaccordance with the invention. The article of manufacture containing thecomputer programming code is used by either executing the code directlyfrom the storage device, by copying the code from the storage deviceinto another storage device such as a hard disk, random access memory(RAM), etc., or by transmitting the code for remote execution. Themethod form of the invention may be practiced by combining one or moremachine-readable storage devices containing the code according to thepresent disclosure with appropriate standard computer hardware toexecute the code contained therein. An apparatus for practicing thetechniques of the present disclosure could be one or more computers andstorage systems containing or having network access to computerprogram(s) coded in accordance with the present disclosure.

Although the invention is described herein with reference to specificembodiments, various modifications and changes can be made withoutdeparting from the scope of the present invention as set forth in theclaims below. For example, the control channel scheduling techniquesdisclosed herein are generally broadly applicable to wirelesscommunication systems. Accordingly, the specification and figures are tobe regarded in an illustrative rather than a restrictive sense, and allsuch modifications are intended to be included with the scope of thepresent invention. Any benefits, advantages, or solution to problemsthat are described herein with regard to specific embodiments are notintended to be construed as a critical, required, or essential featureor element of any or all the claims.

Unless stated otherwise, terms such as “first” and “second” are used toarbitrarily distinguish between the elements such terms describe. Thus,these terms are not necessarily intended to indicate temporal or otherprioritization of such elements.

1. A method of operating a wireless communication system, comprising:determining respective geometries of multiple subscriber stations withrespect to a serving base station, the multiple subscriber stationsincluding a first subscriber station and a second subscriber station;and scheduling, based on the determining the respective geometries,respective control channels for the multiple subscriber stations, therespective control channels including a first control channel associatedwith the first subscriber station and a second control channelassociated with the second subscriber station, wherein the first controlchannel is scheduled to be encountered earlier in a control channelsearch procedure of one or more control channel symbols than the secondcontrol channel, and wherein the first subscriber station has a lowergeometry than the second subscriber station.
 2. The method of claim 1,further comprising: scheduling, based on the determining the respectivegeometries, the first control channel in a first control channel symbol,included within the one or more control channel symbols, of a downlinksubframe.
 3. The method of claim 2, further comprising: scheduling,based on the determining the respective geometries, the second controlchannel in a second control channel symbol, included within the one ormore control channel symbols, of the downlink subframe.
 4. The method ofclaim 1, wherein the first control channel includes a first uplinkcontrol channel, a first downlink control channel, or both the firstuplink control channel and the first downlink control channel, andwherein the second control channel includes a second uplink controlchannel, a second downlink control channel, or both the second uplinkcontrol channel and the second downlink control channel.
 5. The methodof claim 4, wherein the first uplink control channel includes a firstuplink subcarrier assignment and a first uplink slot assignment and thefirst downlink control channel includes a first downlink subcarrierassignment and a first downlink slot assignment, and wherein the seconduplink control channel includes a second uplink subcarrier assignmentand a second uplink slot assignment and the second downlink controlchannel includes a second downlink subcarrier assignment and a seconddownlink slot assignment.
 6. The method of claim 1, wherein therespective geometries correspond to respective carrier to interferenceand noise ratios and the determining further comprises: determining therespective carrier to interference and noise ratios associated with eachof the multiple subscriber stations at the serving base station, whereina first carrier to interference and noise ratio associated with thefirst subscriber station is lower than a second carrier to interferenceand noise ratio associated with the second subscriber station.
 7. Themethod of claim 1, wherein the one or more control channel symbols areorthogonal frequency division multiplexing (OFDM) signals.
 8. The methodof claim 1, further comprising: transmitting the one or more controlchannel symbols, wherein the first control channel provides an assigneduplink, an assigned downlink, or both the assigned uplink and downlinkfor the first subscriber station.
 9. A method of operating a wirelesscommunication system, comprising: receiving, at a first subscriberstation, one or more control channel symbols, the one or more controlchannel symbols including a first control channel associated with thefirst subscriber station and a second control channel associated with asecond subscriber station; and searching the one or more control channelsymbols for the first control channel, wherein the first control channelis scheduled such that the first control channel is encountered earlierin a control channel search procedure than the second control channel,and wherein the first subscriber station has a lower geometry than thesecond subscriber station.
 10. The method of claim 9, wherein the firstcontrol channel includes a first uplink control channel, a firstdownlink control channel, or both the first uplink control channel andthe first downlink control channel, and wherein the second controlchannel includes a second uplink control channel, a second downlinkcontrol channel, or both the second uplink control channel and thesecond downlink control channel.
 11. The method of claim 10, wherein thefirst uplink control channel includes a first uplink subcarrierassignment and a first uplink slot assignment and the first downlinkcontrol channel includes a first downlink subcarrier assignment and afirst downlink slot assignment, and wherein the second uplink controlchannel includes a second uplink subcarrier assignment and a seconduplink slot assignment and the second downlink control channel includesa second downlink subcarrier assignment and a second downlink slotassignment.
 12. The method of claim 9, wherein the control channelsearch procedure is a blind search procedure.
 13. The method of claim 9,wherein a first carrier to interference and noise ratio associated withthe first subscriber station is lower than a second carrier tointerference and noise ratio associated with the second subscriberstation.
 14. The method of claim 9, further comprising: receiving anuplink assignment, a downlink assignment, or both the uplink anddownlink assignments in the first and second control channels for thefirst and second subscriber stations, respectively.
 15. The method ofclaim 9, wherein the first control channel provides a first assigneduplink for the first subscriber station and the method furthercomprises: transmitting, from the first subscriber station, first uplinkinformation in the first assigned uplink.
 16. The method of claim 9,wherein the first control channel provides a first assigned downlink forthe first subscriber station and the method further comprises:receiving, at the first subscriber station, first downlink informationin the first assigned downlink.
 17. The method of claim 9, wherein theone or more control channel symbols are orthogonal frequency divisionmultiplexing (OFDM) signals.
 18. A wireless communication system,comprising: a base station configured to determine respective geometriesof multiple subscriber stations with respect to the base station, themultiple subscriber stations including a first subscriber station and asecond subscriber station; and a scheduler configured to schedulerespective control channels for the multiple subscriber stations basedon the respective geometries of the multiple subscriber stations, therespective control channels including a first control channel associatedwith the first subscriber station and a second control channelassociated with the second subscriber station, wherein the first controlchannel is scheduled to be encountered earlier in a control channelsearch procedure of one or more control channel symbols than the secondcontrol channel, and wherein the first subscriber station has a lowergeometry than the second subscriber station.
 19. The wirelesscommunication system of claim 18, wherein the first control channelincludes a first uplink control channel, a first downlink controlchannel, or both the first uplink control channel and the first downlinkcontrol channel.
 20. The wireless communication system of claim 19,wherein the first uplink control channel includes a first uplinksubcarrier assignment and a first uplink slot assignment and the firstdownlink control channel includes a first downlink subcarrier assignmentand a first downlink slot assignment.
 21. The wireless communicationsystem of claim 18, wherein the one or more control channel symbols areorthogonal frequency division multiplexing (OFDM) signals.
 22. Thewireless communication system of claim 18, wherein the respectivegeometries correspond to respective carrier to interference and noiseratios and the base station is further configured to determine therespective carrier to interference and noise ratios associated with eachof the multiple subscriber stations, and wherein the respective carrierto interference and noise ratio associated with the first subscriberstation is lower than the respective carrier to interference and noiseratio associated with the second subscriber station.